Implantable medical devices (IMDs), including pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g., P-waves and R-waves. Episodes of bradycardia, tachycardia and/or fibrillation are detected from the sensed cardiac events and responded to as needed with pacing therapy or high-voltage cardioversion/defibrillation therapy. Reliable detection and treatment of potentially life-threatening ventricular tachycardia (VT) and ventricular fibrillation (VF) requires reliable sensing of cardiac signals.
Dislodgement or dislocation of a cardiac lead carrying electrodes for sensing EGM signals reduces reliable sensing and could result in erroneous sensing of cardiac signals, leading to improper detection of the cardiac rhythm and inappropriate delivery or withholding of pacing or shock therapy. While an occurrence of ventricular lead dislodgement is rare, such dislodgement could potentially cause inappropriate shock therapy to be delivered. For example, in some rare instances of a ventricular lead dislodging or being dislodged during an episode of atrial fibrillation, cardiac signals associated with the atrial fibrillation episode may be inappropriately sensed as ventricular signals, causing inappropriate detection of a ventricular fibrillation episode and the resultant delivery of therapy. In other instances, improper detection of the cardiac rhythm may cause a necessary or optimal therapy to not be delivered, such as bradycardia pacing or anti-tachycardia pacing. Accordingly, it is desirable to provide an implantable medical device and associated medical device system that is capable of detecting ventricular lead dislodgement during episodes of atrial fibrillation.